Yes, by using multiple calibrations in the MoistScan® (up to 4 separate calibrations can be utilised by
default with the option of 50 calibrations in total) it is as easy as switching a remote calibration switch
either from the control room or on the MoistScan’s control panel for different products.
The Moistscan measures both free and inherent moisture together as total moisture but each has different measurement sensitivities. This must be correctly taken into consideration in the calibration process.
The Moistscan has proven itself on conductive materials, however it is best to check with one of our engineers to ensure you are going to have the best product that suits your requirements. We may be able to assist with one of our NFA enabled Moistscan analysers if the material is highly conductive.
The MoistScan® employs a patented technique that differentiates it from its competitors. Using a
combination of attenuation/phase shift of the microwave signal and dielectric discrimination
techniques, the MoistScan® will provide the end user with consistently reliable results.
Fine coal typically has a dielectric constant of between 2 to 4 compared to the dielectric constant
of water of 80.4. The variation of water within the coal results in a large variation in the combined
dielectric constant which may then be measured by monitoring the change in the microwave signal. Both
the change in velocity (phase shift) and the change in power (attenuation) of the received microwave
signal are affected by the change in the dielectric constant of the analysed material. The microwave
measurement is affected mainly by the excitation of free moisture molecules rather than many other types
of materials, due to the extremely high dielectric constant of water.
Measurement of moisture content in bulk materials using microwaves has been investigated extensively over the past 20 years. Moisture measurement using this technique is based upon the relatively high dielectric constant of water in comparison to the dielectric properties of other materials.
Ideally the presentation of the material should be uniform; however slight changes in presentation should
not pose any problems with maintaining reliable results. If material upon a conveyor is not centred
correctly, or is badly profiled, then a leveler bar could be installed to improve the material profile.
The microwave principle employed by the MoistScan® is a full penetration technique which means the
product is fully scanned for moisture content as opposed to NIR, which is basically a surface technique
using an infra red light beam. The results of a NIR gauge is adversely affected by colour variations, ambient
lighting, and presence of dust and temperature variations. The MoistScan® is unaffected by any of
these anomalies, thus the MoistScan® will give a more accurate indication of the free moisture within the
The MoistScan® has proven itself to be reliable, repeatable and much more cost effective than any
similar Nucleonic based moisture analysers. Other advantages are: No radioactive sources in the
MoistScan®, which means no red tape associated with getting radioactive sources government approved
and ultimately it is a safer more environmentally friendly gauge.
The more samples taken, the more confidence placed in the calibration. Many statistical measures have
little confidence below sets of less than 30 samples. If taking 30 samples is not feasible, then as many
samples as can be taken. To increase the level of confidence from a set of samples, they should be
analysed more than once.
Under normal operating conditions, the MoistScan® should not require re-calibration unless product
presentation is significantly altered. However Callidan do suggest some check samples be taken every
three months to confirm accuracy.
The ultrasonic depth sensor is satisfactory for most applications that involve moderate variations in
bulk density. It is, however, limited in applications that have very dense material combined with large
variations in bulk density. In these applications we take an input from a weightometer or similar mass
throughput sensor to compensate for the density effects.
Using the ultrasonic depth sensor on the MoistScan® the analyser can be programmed to ignore
bed depths that exceed the maximum bed depth for the product. The unit will automatically re-commence
analysing once the bed depth is back within the normal operating range. This answer also applies to
bed depths that fall below a pre-programmed minimum depth.
The microwave technique penetrates through all the product material on the conveyor, so there is no
adverse effects of product segregation. This segregation may have an affect how representative samples
taken from the conveyor are.
The MoistScan® MA-500 On-Belt Moisture Analyser is designed to use low level non-ionizing microwave
radiation. The microwave power emitted from the MOISTSCAN MA-500 is less than 10 mW (10 dBm).
This complies with AS/NZS 4268 which specifies the maximum Equivalent Isotropically Radiated Power
(EIRP) for short range radio equipment. Furthermore, this radiation level exists directly between the two
antennas, which in almost all cases is inaccessible due to the conveyor belt. Microwave radiation further
than 1 m from the analyser is virtually undetectable.
Precision is a gauge of the deviation within a set of measurements. In this case, it is the repeatability
of moisture content measurement. It is expressed as the standard deviation of a number of measurements
of the same sample.
Accuracy is a gauge of the deviation between a measurement and the value of the property being
measured. In this case, it is the deviation between the MoistScan® results and the laboratory results for
a set of samples. It is expressed as the standard deviation of the differences between analyser and
Factors that influence highly accurate results are: Minimal spread of moisture range. (The tighter the range
the more accurate the instrument will be), even material presentation on the transport medium,
representative sampling, careful handling of samples and prompt analysis. The analysis procedure should
consume all of the sample.
Magnetite concentrate and magnetite ore have proved to be difficult applications for the standard MoistScan® transmission technology. This is chiefly due to the magnetic nature or magnetic permeability of the product. The magnetic permeability is the degree of magnetization of a material in response to a magnetic field.
Put simply, the microwave transmission signal is largely affected by the water within the Ore/Concentrate BUT unfortunately also affected by the magnetic permeability of the product. This is a problem because we cannot distinguish the moisture changes from the magnetic permeability changes.
Recently Callidan has developed an analyser which will overcome these difficulties. We call it NFA
(Near Field Analysis) but it is simply a direct measure of the magnetic susceptibility and microwave
response (via reflection) of the material. It is called “Near Field Analysis” because the analysis zone
will only penetrate the lower portion of the product upon the conveyor and NOT all the product like our
previous transmission technique.
The reliability of original lab samples, the presentation of the material (if inconsistent) and some environmental factors. All these factors can be overcome by providing as much information as possible so our engineers can find a suitable installation point where theses factors can be reduced or eliminated.
Consistency and better accuracy over other types of methods. eg: NIR (near infra red), microwave
technology is safe and reliable, unaffected by material presentation & colour variations, etc.
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